The present invention relates to hydrofoils of the type used for propulsion in a fluid medium, and more particularly to swim fins.
Swim fins are used by swimmers, body surfers, divers and others in water to improve propulsion speed and water agility. Swim fin designs that combine a foot pocket with side rails and a propulsion blade are commercially available. The objective of a swim fin design is to provide maximum propulsion and agility while minimizing the work expended by the swimmer. This may be accomplished by optimizing the angle of attack of the fin blade during the up and down strokes of the swimmer's kick propelling him through the water. Typical swim fins currently available are either too rigid or too flexible for a given use, or have contours or profiles that result in inefficient hydrodynamics where water spills over the sides of the fin blade, or generate fluid vortices that may negate lift or propulsive forces resulting in a decrease in swimming efficiency with a corresponding increase in swimmer fatigue. For optimum propulsion it is desired for water flow to be laminar and essentially free of excess turbulence.
The “angle of attack” of a fin blade may be defined as the angle between the line of horizontal movement of the swimmer's body through the water and the lengthwise alignment of the fin blade relative to the line of horizontal movement. Swim fin performance may be optimized for various modes of use. For example, available swim fins may be designed for low, moderate or aggressive kicking. For recreational or relaxed use, the swim fin may be constructed of flexible material to provide a low angle of attack for efficient low thrust operation. For aggressive kicking, the swim fin may be constructed of stiff material to provide a high angle of attack for efficient high thrust operation. A proper angle of attack may optimize the conversion of kicking energy of the swimmer to thrust or propulsion through the water. Aggressive and nonaggressive modes of use generally required different fin designs and/or different fin material durometers because optimum fin performance for each mode requires mutually exclusive design parameters. During nonaggressive use a highly flexible fin blade may provide efficient low thrust operation, whereas during aggressive use a rigid fin blade may provide efficient high thrust operation. Other known swim fin designs provide deformable regions permitting the fin blade to flex about a transverse axis.